Micropores in Carbonate Mud:Early Development and Petrophysics

摘要

Micropores are commonly found in mud-dominated fabrics located between microspar and microrhombic calcite. Understanding the development of micropores is important in petroleum geology to facilitate predicting its distribution and reservoir properties in carbonate reservoirs. The diagenetic history of micropore development can be long and complex. Many geologists have emphasized dissolution of low-porosity micrite as the principal process in forming micropores, whereas others have emphasized simple cementation of depositional carbonate mud. This study is focused on the early transformation of a depositional lime mud to a microporous microspar fabric. The material used in this study is from the core taken from well Clino on the western slope of the Great Bahama Bank. Previous investigations of this transformation have concluded that microspar is cemented aragonitic sediment. Results of our study suggest that the initial phase of the transformation is a replacement process with dissolution of micrometer-to nanometer-sized aragonitic/calcitic precursor sediment and precipitation of 1- to 10- micron microspar crystals. No porosity is gained or lost during this process indicating that no carbonate is added to or subtracted from the system. Carbonate is added later in the form of porosity reducing cement. The increase in crystal size has a strong impact on permeability by increasing permeability tenfold without changing porosity.